1. Field of the Invention
The present invention relates to a semiconductor device inspection system for analyzing anomalous occurrences inside a semiconductor device and for evaluating reliability of a semiconductor device, and more particularly to a semiconductor device inspection system for transparently taking an image of inside of a semiconductor device.
2. Related Background Art
As a semiconductor device is highly integrated, e.g., VLSI, difficulty of anomaly analysis and reliability evaluation of internal circuits of the semiconductor device is increased.
In such present condition, much attention is focused on the analysis technology to track down the location of an anomalous portion by detecting very weak light emitted from the anomalous portion in semiconductor device. An emission microscope is known as a semiconductor device inspection apparatus utilizing such analysis technology.
The emission microscope picks up very weak light caused by hot carriers, which are produced when an electric field is concentrated on an anomalous portion in semiconductor device, or very weak light in the infrared region caused by latchup. Therefore, the emission microscope can measure a semiconductor device to be checked without contact and with high accuracy.
However, the emission microscope has such a problem that since it detects emitted light in the visible to infrared region, it could become incapable of measuring emitted light if there would exist some shielding object between an anomalous portion emitting very weak light and the emission microscope.
In particular, in order to make a semiconductor device being highly integrated, semiconductor devices tend to employ the chip structure in which interconnection between numerous elements such as transistors is made by multilayer wiring located on the top surface. The multilayer wiring interrupts the very weak light caused by an anomaly of an element underneath the multilayer wiring, which caused a problem of inability of measurement or not permitting high-accuracy measurement. In semiconductor devices to which the so-called Lead On Chip packaging structure is applied, a lead frame covers the top surface of the semiconductor chip. For such devices, similarly to the case of the multilayer wiring, the lead frame will be a shielding object and interrupt the very weak light, resulting in inability of measurement or not permitting high-accuracy measurement.
Further, there is another problem in applications of the emission microscope. For example, it is known as an observing method that a top surface of a plastic mold is chemically removed, e.g., by fuming nitric acid to expose the surface of semiconductor chip and when a predetermined bias power source is connected to a lead frame to supply power to internal circuits of the semiconductor chip, very weak light is emitted from an anomalous portion, which is observed from the top surface of the semiconductor chip. However, when the plastic mold is chemically removed, e.g., by fuming nitric acid, the circuit patterns or others inside the semiconductor chip could be damaged, which could hinder observation of an anomalous portion to be observed originally.
To solve these problems of emission microscopes, a semiconductor device inspection system (Japanese Patent Application No. HEI 5-177957 (177957/1993)) was developed. This inspection system is to illuminate the back surface of a semiconductor device, that is, the back surface where shielding objects such as multilayer wiring of the semiconductor chip are not formed, by an infrared-ray epi-illumination means and to take an optical image reflected and transmitted through the semiconductor chip. Therefore, an observed image specifying an anomalous location in the semiconductor chip can be obtained. However, even with this semiconductor device inspection system, still there were problems to be solved, e.g., large noise components, in order to obtain a clearer image.